Cystic Fibrosis (CF) is one of the most common inherited fatal diseases. Over the past thirty years, the median age of survival has improved from 14 years in 1969 to 29.1 years (95% Cl's 27.5 to 31.6) in 1999 in the United States. With this improved survival, this disease has been transformed from a disease with very high infant mortality to a disease that must now be considered a chronic and progressive lung disease. Improving the survival in these patients has been the primary goal over the last 30 years, but now clinical researchers must broaden their assessment of outcome in this disease to include patient-oriented outcomes such as health-related quality of life. Unfortunately, there is very limited research on the utility and relative strengths of different methods to measure health-related quality of life in patients with CF, especially for that group with the most severe disease. A better understanding of the best instruments, the minimal clinically important difference of these instruments, and the course of quality of life in these patients is needed in order to assess the value of treatments and interventions and to counsel patients and their families about their prognosis and the morbidity associated with this disease. This application proposes a prospective cohort study of patients with severe CF. Four different health-related quality of life instruments will be assessed, including a recently developed CF specific quality of life instrument. Patients will be evaluated at 6 month intervals f or a total of three years. The overall object of this proposal is to advance the state of the art in the measurement of health-related quality of life in adolescent and adult patients with severe cystic fibrosis in order to facilitate development and assessment of treatments that improve the quality of patients' lives and help predict the best time for evaluation for a lung transplant. In addition, this application proposes to compare the baseline differences health-related quality of life in patients not listed for lung or heart lung transplant, listed for lung or heart lung transplant, and transplanted and how health-related quality of life changes through time in these patients.